Various silicone containing monomers have found utility as starting materials in the production of medical devices, such as ophthalmic devices and particularly, soft contact lenses having improved permeability to oxygen. One class of suitable monomers includes tris and bis(trimethylsilyloxy)silylalkylglycerol methacrylates (“SiAGMA”). During the synthesis of SiAGMA certain diester acrylate impurties are also generated. The diester acrylates or free radical reactive difunctional groups act as crosslinkers during the polymerization of the SiAGMAs with other polymer forming components. Accordingly, the concentration of the diester acrylates must be controlled to ensure that the mechanical properties of the resulting medical device do not vary to an unacceptable degree.
Classical methods for preparing 1,2-diesters involve the treatment of 1,2-diols with acid chlorides or anhydrides in the presence of a base. However, functional groups such as trimethylsilyl ethers are sensitive to such conditions and additional purification is required to obtain the desired product(s) in high purity. One method for the production of vicinal diesters use an amine to catalyze the nucleophilic opening of the epoxide in the presence of an anhydride and methacrylic acid to form a partially acylated mixture of compounds containing a vicinal methacrylate. The difunctional free radical impurities that are made during the course of producing the monofunctional free radical reactive monomer have to be controlled using either a different synthetic pathway or the use of various purification steps. The free radical reactive functional groups in the monomeric materials are made and then rely heavily on various modes of post synthesis purification methodology.
Accordingly, there remains a need in the art for a process which can produce vicinal diesters in high yield and purity.